This code appears in the following versions (click to see it in the source code):
Code variations between these versions are shown below.
Name: Main flight loop (Part 3 of 16) Type: Subroutine Category: Main loop Summary: Scan for flight keys and process the results Deep dive: Program flow of the main game loop The key logger
The main flight loop covers most of the flight-specific aspects of Elite. This section covers the following: * Scan for flight keys and process the results Flight keys are logged in the key logger at location KY1 onwards, with a non-zero value in the relevant location indicating a key press. See the deep dive on "The key logger" for more details. The key presses that are processed are as follows: * Space and "?" to speed up and slow down * "U", "T" and "M" to disarm, arm and fire missiles
* ESCAPE to launch an escape pod * "J" to initiate an in-system jump * "E" to deploy E.C.M. anti-missile countermeasures * "C" to use the docking computer * "A" to fire lasers
LDA KY2 \ If Space is being pressed, keep going, otherwise jump BEQ MA17 \ down to MA17 to skip the following LDA DELTA \ The "go faster" key is being pressed, so first we CMP #40 \ fetch the current speed from DELTA into A, and if BCS MA17 \ A >= 40, we are already going at full pelt, so jump \ down to MA17 to skip the following INC DELTA \ We can go a bit faster, so increment the speed in \ location DELTA .MA17 LDA KY1 \ If "?" is being pressed, keep going, otherwise jump BEQ MA4 \ down to MA4 to skip the following DEC DELTA \ The "slow down" key is being pressed, so we decrement \ the current ship speed in DELTA BNE MA4 \ If the speed is still greater than zero, jump to MA4 INC DELTA \ Otherwise we just braked a little too hard, so bump \ the speed back up to the minimum value of 1 .MA4 LDA KY15 \ If "U" is being pressed and the number of missiles AND NOMSL \ in NOMSL is non-zero, keep going, otherwise jump down BEQ MA20 \ to MA20 to skip the following
The Master version has a unique "low beep" sound that has more reverb than in the other versions.
Tap on a block to expand it, and tap it again to revert.
LDA #0 \ Set MSAR to 0 to indicate that no missiles are STA MSAR \ currently armed .MA20 LDA MSTG \ If MSTG is positive (i.e. it does not have bit 7 set), BPL MA25 \ then it indicates we already have a missile locked on \ a target (in which case MSTG contains the ship number \ of the target), so jump to MA25 to skip targeting. Or \ to put it another way, if MSTG = &FF, which means \ there is no current target lock, keep going LDA KY14 \ If "T" is being pressed, keep going, otherwise jump BEQ MA25 \ down to MA25 to skip the following LDX NOMSL \ If the number of missiles in NOMSL is zero, jump down BEQ MA25 \ to MA25 to skip the following STA MSAR \ The "target missile" key is being pressed and we have \ at least one missile, so set MSAR = &FF to denote that \ our missile is currently armed (we know A has the \ value &FF, as we just loaded it from MSTG and checked \ that it was negative)
.MA25 LDA KY16 \ If "M" is being pressed, keep going, otherwise jump BEQ MA24 \ down to MA24 to skip the following
JSR FRMIS \ The "fire missile" key is being pressed and we have \ a missile lock, so call the FRMIS routine to fire \ the missile .MA24
This variation is blank in the Cassette, Disc (flight), 6502 Second Processor and Electron versions.
LDA BOMB \ If we already set off our energy bomb, then BOMB is BMI MA76 \ negative, so this skips to MA76 if our energy bomb is \ already going off
ASL BOMB \ The "energy bomb" key is being pressed, so double \ the value in BOMB. If we have an energy bomb fitted, \ BOMB will contain &7F (%01111111) before this shift \ and will contain &FE (%11111110) after the shift; if \ we don't have an energy bomb fitted, BOMB will still \ contain 0. The bomb explosion is dealt with in the \ MAL1 routine below - this just registers the fact that \ we've set the bomb ticking
The Master's energy bomb lightning bolt effect contains nine random zig-zag lines that are set up in the BOMBON routine.
This variation is blank in the Cassette, Disc (flight), 6502 Second Processor and Electron versions.
BEQ MA76 \ If BOMB now contains 0, then the bomb is not going off \ any more (or it never was), so skip the following \ instruction JSR BOMBON \ Call BOMBON to set up and display a new energy bomb \ zig-zag lightning bolt
.MA76
In the enhanced versions, the main loop scans for "P" being pressed, which disables the docking computer.
This variation is blank in the Cassette and Electron versions.
Tap on a block to expand it, and tap it again to revert.
In the original versions, you can launch your escape pod in witchspace (though it may be fatal, depending on the version). You can't even launch it in the advanced versions, as the launch key is disabled in witchspace.
This variation is blank in the Cassette, Disc (flight) and Electron versions.
LDA MJ \ If we are in witchspace, we can't launch our escape BNE noescp \ pod, so jump down to noescp
JMP ESCAPE \ The button is being pressed to launch an escape pod \ and we have an escape pod fitted, so jump to ESCAPE to \ launch it, and exit the main flight loop using a tail \ call
LDA KY18 \ If "J" is being pressed, keep going, otherwise skip BEQ P%+5 \ the next instruction JSR WARP \ Call the WARP routine to do an in-system jump LDA KY17 \ If "E" is being pressed and we have an E.C.M. fitted, AND ECM \ keep going, otherwise jump down to MA64 to skip the BEQ MA64 \ following LDA ECMA \ If ECMA is non-zero, that means an E.C.M. is already BNE MA64 \ operating and is counting down (this can be either \ our E.C.M. or an opponent's), so jump down to MA64 to \ skip the following (as we can't have two E.C.M. \ systems operating at the same time) DEC ECMP \ The E.C.M. button is being pressed and nobody else \ is operating their E.C.M., so decrease the value of \ ECMP to make it non-zero, to denote that our E.C.M. \ is now on JSR ECBLB2 \ Call ECBLB2 to light up the E.C.M. indicator bulb on \ the dashboard, set the E.C.M. countdown timer to 32, \ and start making the E.C.M. sound .MA64
If "C" is pressed during flight and we have a docking computer, then in the enhanced versions the docking computer takes control of the ship, unlike in the cassette version, which instantly docks when "C" is pressed.
Tap on a block to expand it, and tap it again to revert.
This variation is blank in the Cassette, Disc (flight), 6502 Second Processor and Electron versions.
\EOR KLO+&29 \ These instructions are commented out in the original \BEQ MA68 \ source \STA auto \JSR startbd
.MA68
This variation is blank in the Cassette, Disc (flight), 6502 Second Processor and Electron versions.
\kill phantom Cs \ This comment appears in the original source
LDA #0 \ Set LAS = 0, to switch the laser off while we do the STA LAS \ following logic STA DELT4 \ Take the 16-bit value (DELTA 0) - i.e. a two-byte LDA DELTA \ number with DELTA as the high byte and 0 as the low LSR A \ byte - and divide it by 4, storing the 16-bit result ROR DELT4 \ in DELT4(1 0). This has the effect of storing the LSR A \ current speed * 64 in the 16-bit location DELT4(1 0) ROR DELT4 STA DELT4+1 LDA LASCT \ If LASCT is zero, keep going, otherwise the laser is BNE MA3 \ a pulse laser that is between pulses, so jump down to \ MA3 to skip the following LDA KY7 \ If "A" is being pressed, keep going, otherwise jump BEQ MA3 \ down to MA3 to skip the following LDA GNTMP \ If the laser temperature >= 242 then the laser has CMP #242 \ overheated, so jump down to MA3 to skip the following BCS MA3 LDX VIEW \ If the current space view has a laser fitted (i.e. the LDA LASER,X \ laser power for this view is greater than zero), then BEQ MA3 \ keep going, otherwise jump down to MA3 to skip the \ following \ If we get here, then the "fire" button is being \ pressed, our laser hasn't overheated and isn't already \ being fired, and we actually have a laser fitted to \ the current space view, so it's time to hit me with \ those laser beams PHA \ Store the current view's laser power on the stack AND #%01111111 \ Set LAS and LAS2 to bits 0-6 of the laser power STA LAS STA LAS2
The Master version has a unique sound for when our laser is firing.
Tap on a block to expand it, and tap it again to revert.
JSR LASLI \ Call LASLI to draw the laser lines PLA \ Restore the current view's laser power into A BPL ma1 \ If the laser power has bit 7 set, then it's an "always \ on" laser rather than a pulsing laser, so keep going, \ otherwise jump down to ma1 to skip the following \ instruction
.ma1 AND #%11111010 \ LASCT will be set to 0 for beam lasers, and to the STA LASCT \ laser power AND %11111010 for pulse lasers, which \ comes to 10 (as pulse lasers have a power of 15). See \ MA23 below for more on laser pulsing and LASCT